27... d6c6  28. a2c3 The knight is well placed on this square, decreasing the strength of a5-a4, and planning to land on b5. 28... d7b6  29. f2f4 White's idea is logical—to gain space in the center and on the kingside. He follows the old strategy of the \"principle of two weaknesses,\" so well explained in the classic book \"Endgame Strategy\" by renowned author Mikhail Shereshevsky, and also by Mark Dvoretsky in several of his books. It's impossible to win just by attacking the weakness on a6—creating another attacking front is necessary. That said, advancing the pawn to f4 is not the best way to do it. It would be better to start with 29.g4 or 29.h4, reducing the potential of a defensive resource  Black can exploit on the next move. 29... b6c8 